全文获取类型
收费全文 | 1265篇 |
免费 | 65篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 8篇 |
综合类 | 3篇 |
化学工业 | 350篇 |
金属工艺 | 39篇 |
机械仪表 | 31篇 |
建筑科学 | 24篇 |
矿业工程 | 1篇 |
能源动力 | 62篇 |
轻工业 | 77篇 |
水利工程 | 16篇 |
石油天然气 | 7篇 |
无线电 | 142篇 |
一般工业技术 | 357篇 |
冶金工业 | 29篇 |
原子能技术 | 1篇 |
自动化技术 | 195篇 |
出版年
2024年 | 4篇 |
2023年 | 20篇 |
2022年 | 43篇 |
2021年 | 70篇 |
2020年 | 48篇 |
2019年 | 50篇 |
2018年 | 60篇 |
2017年 | 57篇 |
2016年 | 53篇 |
2015年 | 41篇 |
2014年 | 47篇 |
2013年 | 102篇 |
2012年 | 62篇 |
2011年 | 74篇 |
2010年 | 61篇 |
2009年 | 61篇 |
2008年 | 62篇 |
2007年 | 41篇 |
2006年 | 39篇 |
2005年 | 33篇 |
2004年 | 22篇 |
2003年 | 15篇 |
2002年 | 21篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 16篇 |
1997年 | 14篇 |
1996年 | 21篇 |
1995年 | 13篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有1342条查询结果,搜索用时 15 毫秒
81.
Abandoned coal ash ponds cover up vast stretches of precious land and cause environmental problems. Application of suitable in situ stabilization methods may bring about improvement in the geotechnical properties of the ash deposit as a whole, converting it to a usable site. In this study, a technique of in-place stabilization by hydrated lime columns was applied to large-scale laboratory models of ash ponds. Samples collected from different radial distances and different depths of the ash deposit were tested to study the improvements in the water content, dry density, particle size distribution, unconfined compressive strength, pH, hydraulic conductivity, and leachate characteristics over a period of one year. The in-place stabilization by lime column technique has been found effective in increasing the unconfined compressive strength and reducing hydraulic conductivity of pond ash deposits in addition to modifying other geotechnical parameters. The method has also proved to be useful in reducing the contamination potential of the ash leachates, thus mitigating the adverse environmental effects of ash deposits. 相似文献
82.
The lattice contribution to the thermal conductivity (κph) in La0.80Ca0.20 MnO3 manganites is discussed within the Debye-type relaxation rate approximation in terms of the acoustic phonon frequency and
relaxation time. The theory is formulated when heat transfer is limited by the scattering of phonons from defects, grain boundaries,
charge carriers, and phonons. The lattice thermal conductivity dominates in La–Ca–MnO manganites and is an artifact of strong
phonon-impurity and -phonon scattering mechanisms in the ferromagnetic metallic state. The electronic contribution to the
thermal conductivity (κe) is estimated following the Wiedemann–Franz law. This estimate sets an upper bound on κe, and in the vicinity of the Curie temperature (240 K) κe is about 1% of total heat transfer of manganites. Another important contribution in the metallic phase should come from spin
waves (κm). It is noticed that κm increases with a T2 dependence on the temperature. These channels for heat transfer are algebraically added and κtot develops a broad peak at about 55 K, before falling off at lower temperatures. The behavior of the thermal conductivity in
manganites is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance
between electron, magnon, and phonon contributions. The numerical analysis of heat transfer in the ferromagnetic metallic
phase of manganites shows similar results as those revealed from experiments.
相似文献
83.
Controlled growth of nano/micro structures by controlling the effective parameters is the basic requirement for the application point of view in various areas. Here we report the facile growth of silver molybdate nano/micro rods by mixing the solution of silver nitrate and ammonium molybdate at ambient condition followed by hydrothermal treatment at various temperatures for 12 h. To achieve the goal for the synthesis of long, high yield and homogeneous nanorods various effective parameters have been studied to set the most effective conditions for the growth. Among possible effective parameters first the temperature of the furnace was set by warring the temperature and then at the set temperature the concentration of reactants (NH4)6Mo7O24 and silver nitrate are varied respect to each other. The pH and temperature values were monitored during the mixing of the reactants. Structural/microstructural characterization revealed the optimum condition of 150°C of the furnace and the concentration of (NH4)6Mo7O24 and silver nitrate as described in various tables. 相似文献
84.
Rajiv Kumar Sharma Dinesh Kumar Pradeep Kumar 《International journal of systems science》2013,44(6):563-581
The main objective of the article is to permit the reliability analyst's/engineers/managers/practitioners to analyze the failure behavior of a system in a more consistent and logical manner. To this effect, the authors propose a methodological and structured framework, which makes use of both qualitative and quantitative techniques for risk and reliability analysis of the system. The framework has been applied to model and analyze a complex industrial system from a paper mill. In the quantitative framework, after developing the Petrinet model of the system, the fuzzy synthesis of failure and repair data (using fuzzy arithmetic operations) has been done. Various system parameters of managerial importance such as repair time, failure rate, mean time between failures, availability, and expected number of failures are computed to quantify the behavior in terms of fuzzy, crisp and defuzzified values. Further, to improve upon the reliability and maintainability characteristics of the system, in depth qualitative analysis of systems is carried out using failure mode and effect analysis (FMEA) by listing out all possible failure modes, their causes and effect on system performance. To address the limitations of traditional FMEA method based on risky priority number score, a risk ranking approach based on fuzzy and Grey relational analysis is proposed to prioritize failure causes. 相似文献
85.
B. Marí K.C. Singh Paula Cembrero-Coca Ishwar Singh Devender Singh Subhash Chand 《Displays》2013,34(4):346-351
Ca (or Sr)TiO3:Eu3+, M (Li+ or Na+ or K+) and CaTiO3:Pr3+, M (Li+ or Na+ or Ag+ or K+ or Gd3+ or La3+) powders were prepared by combustion synthesis method and the samples were further heated to ~1000 °C to improve the crystallinity. The structure and morphology of materials were examined by X-ray diffraction (XRD) and a scanning electron microscopy (SEM). The morphologies of SrTiO3:Eu3+, CaTiO3:Eu3+ or CaTiO3:Pr3+ powders co-doped with other metal ions were very similar. Small and coagulated particles of nearly cubical shapes with small size distribution having smooth and regular surface were formed. Photo-luminescence spectra of CaTiO3:Pr3+ and co-doped either with Li+, Na+, K+, Ag+, La3+ or Gd3+ ions showed red emissions at 613 nm due to the 1D2 → 3H4 transition of Pr3+. The variation of intensity of emission peak with different co-doping follows the order: K+ > Ag+ > Na+ > Li+ > La3+ > Gd3+. The characteristic emissions of CaTiO3:Eu3+ lattices had strong emission at 614 and 620 nm for 5D0 → 7F2 with other weak transitions observed at 580, 592, 654, 705 nm for 5D0 → 7Fn transitions where n = 0, 1, 3, 4 respectively in all host lattices. Photoluminescence intensity in SrTiO3:Eu3+ is more than CaTiO3:Eu3+ lattices. A remarkable increase of photoluminescence intensity (in 5D0 → 7F2 transition) was observed if co-doped with Li+ ions in CaTiO3:Eu3+ and SrTiO3:Eu3+. 相似文献
86.
Chinmay Mallik Shyam Lal Manish Naja Duli Chand S. Venkataramani Hema Joshi 《International journal of remote sensing》2013,34(8):2749-2762
The combustion of fossil fuels (coal and petroleum products) constitutes a source of continuous release of anthropogenic SO2 into the atmosphere. Furthermore, natural sources such as volcanoes can inject large amounts of SO2 directly into the troposphere and sometimes even into the stratosphere. These event-based volcanic eruptions provide solitary opportunities to study the transport and transformation of atmospheric constituents. In this study, we present an episode of high SO2 concentration over northern India as a result of long-range transport from Africa using multiple satellite observations. Monthly averaged column SO2 values over the Indo-Gangetic Plain (IGP) were observed in the range of 0.6–0.9 Dobson units (DU) during November 2008 using observations from the Ozone Monitoring Instrument (OMI). These concentrations were conspicuously higher than the background concentrations (<0.3 DU) observed during 2005–2010 over this region. The columnar SO2 loadings were highest on 6 November over most of the IGP region and even exceeded 6 DU, a factor of 10–20 higher than background levels in some places. These enhanced SO2 levels were not reciprocated in satellite-derived NO2 or CO columns, indicating transport from a non-anthropogenic SO2 source. As most of the local aerosols over the IGP region occur below 3 km, a well-separated layer at 4–5 km was observed from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. Wind fields and back-trajectory analysis revealed a strong flow originating from the Dalaffilla volcanic eruption in Ethiopia during 4–6 November 2008. Although volcanic SO2 plumes have been extensively studied over many parts of Asia, Europe, and the USA, analysis of such events for the IGP region is being reported for the first time in this study. 相似文献
87.
88.
89.
K.A. Venkatesan Dinesh K. Patre K.N. Sabharwal T.G. Srinivasan P.R. Vasudeva Rao 《溶剂提取与离子交换》2013,31(3):551-565
ABSTRACT The rate of extraction of uranium by macroporous bifunctional phosphinic acid (MPBPA) resin from nitric acid medium has been studied under particle diffusion controlled conditions. The internal diffusion coefficient was found to increase with increase in temperature and decrease with increase in particle size. The activation energies and entropies suggest that the extraction of uranium essentially follows ion exchange mechanism at low concentration of nitric acid while it is through linkage of >P=0 group of the resin at high concentrations. 相似文献
90.
Pramod S. Dobal Rasmi R. Das Ram S. Katiyar Dinesh C. Agrawal 《Journal of the American Ceramic Society》2000,83(8):1953-1956
Powder compacts of TiO2 and ZrO2 were prepared from their suspensions in water at different pH values, and micro-Raman spectroscopy was used to reveal the degree of mixing in each of them, with different sizes of the focused laser spot. The change in laser intensity and particle-size distributions led to a slight variation in the average composition, as determined using three different probe sizes. The Raman-estimated volume fractions of each constituent indicated that the aqueous suspensions in which the powders were well dispersed produced the most-uniform mixing. Powders that were flocculated in suspensions before mixing also resulted in a good mixture. The most-nonuniform mixing was observed when, in the individual suspensions, one of the constituents was dispersed and the other was flocculated. These results indicated that Raman spectroscopy can be useful for the rapid determination of the degree of mixing in powder mixtures. 相似文献